Improve uploading and hover experience of designs app

Follow up from !37171 (comment 381264301). @ntepluhina commented:

Let's select the preferable option and implement it via this MR to fix users' issue with pasting designs, and I believe we could iterate on this to achieve the desired UI/UX.

We should discuss ways to improve this hover state for the Designs section.

Current hover state:

Axure Prototype: https://s809ix.axshare.com

Relevant MRs:

• MR that introduced the change: !37171 (merged)
• Follow up MR to remove border: !37375 (merged) (cc @mvanremmerden)